A biosensor is a sensor for determining a quantity of a base substance in a sample solution, which utilizes a molecule recognizing ability of a biological material such as micro-organism, enzyme, antibody, DNA, RNA or the like to employ the biological material as a molecule discrimination element. To be specific, the biosensor determines a quantity of a base substance contained in a sample solution by utilizing a reaction which occurs when a biological material recognizes an objective substrate, such as consumption of oxygen due to respiration of a micro-organism, enzyme reaction, light emission, and the like. Among various kinds of biosensors, an enzyme sensor has come into practical use. For example, an enzyme sensor as a biosensor for glucose, lactic acid, cholesterol, or amino acid has been utilized for medical analysis and food industry. In this enzyme sensor, an electron carrier is reduced by electrons that are generated due to a reaction between a base substance included in a sample solution as an analyte and enzyme or the like, and a measurement unit electrochemically measures a reduction quantity of the electron carrier, thereby performing quantitative analysis for the sample.
There have been proposed various types of biosensors. For example, as a biosensor that facilitates measurement of a blood glucose level, there is a biosensor comprising a first insulating substrate on which a pair of electrodes and a reagent layer are formed, a second insulating substrate bonded to the first insulating substrate via a spacer, and a capillary for collecting a sample solution, which is provided between the both insulating substrates. The biosensor is constituted such that blood obtained by puncturing the human body is introduced by capillary phenomenon into the capillary from a sample supply port that opens at one ends of the both substrates.
In this biosensor, however, there is a possibility that the blood is not successfully introduced into the capillary depending on the angle of the biosensor when the blood is applied onto the sample supply port, and thereby the blood might be attached to the outer surface of the insulating substrate by mistake. In this case, even when the user tries to supply the blood again, the blood attached to the outer surface impedes the user from successfully supplying the blood into the capillary, resulting in faulty measurement and measurement errors.
In order to solve this problem, the inventors of the present invention have proposed a biosensor in which the ends of the both substrates which constitute the sample supply port are formed in different shapes when viewed planarly so that blood can always be introduced into the capillary successfully without being influenced by the angle of the biosensor when the blood is applied (refer to Patent Document 1).
FIG. 8 illustrates an exploded perspective view and a cross-sectional view of the biosensor disclosed in Patent Document 1. In FIG. 8, reference numeral 1 denotes a first insulating substrate, and a measurement electrode 2, a counter electrode 3, and a detector electrode 4, which comprise an electric conducting material, are formed on the first insulating substrate 1.
The conventional biosensor 800 is formed by bonding the first insulating substrate 1, a spacer 6, and a second insulating substrate 8 together, and a capillary 7 is formed by the existence of a notch in the spacer 6. A test sample is introduced into the capillary 7 from its front end by a sample supply port 13 that is formed by the bonding and an air hole 9 formed through the insulating substrate 1.
Further, the measurement electrode 2, the counter electrode 3, and the detector electrode 4 which are formed on the first insulating substrate 1 are exposed in the capillary 7, and a reagent layer 5 is formed in a position opposed to these electrodes.
A measurement instrument (not shown) having terminals to be connected to leads 10, 11, and 12 of the electrodes is inserted in the biosensor before introduction of blood, and variation in the electric characteristics which occurs due to a reaction of the blood with the reagent is detected between the measurement electrode 2 and the counter electrode 3 after introduction of blood, thereby measuring a glucose concentration.    Patent Document 1: Japanese Published Patent Application No. 2002-168821).